Production of pulp



Patented Feb. 9, 1926.

UNITED STATES PATENT OFFICE.

LINN BRADLEY, E MONTGLAIR, NEW JERSEY, Aim DWARD P. McKEEFE, or PLATTS-BURG, NEW YORK.

PRonuo'rroN 0E PULP.

No Drawing. Original application filed March 28, 1921, SerialNo.'456,187. Divided and this application filed April 10, 19-24. SerialNo.'7 05,711.

respectively, have invented certain new and useful Improvements in theProduction of Pulp; and we do hereby declare the following to be a full,clear, and exact descrlptlon of the invention, such as will enableothers skilled in the art to which it make and use the same.

This invention relates to improvements in processes of cogking woodchips and similar material for the production of Wood cellu loseproducts or pulp.

The present invention includes a new method of cookin or digesting Woodchips in'ivhich the cooking liquor is an alkaline liquor containing athiosulfate of an alkali, or both a sulfite and a thiosulfate of analkali. This method is distinguished by the fact that caustic soda ispresent in sufficient amounts to give an alkaline cooking liquor ofappropriate strength, while sodium thioappertains, to

sulfate,'or both sodium sulfite and sodium thiosulfate, is or are alsopresent in substantial amounts. The composite cooking "liquor,containing caustic soda and sodium thiosulfate, or containing causticsoda together with sodium sufite and sodium thiosulfate,' can varysomewhat in, its composi tion and in the proportions of caustic soda andof sodium thiosulfate, or of sodium thiosulfate and sodium sulfite.Ordinarily a preponderating proportion of caustic soda will be used,forexample, so that from 50 to 90% of the total sodium of the cooking 40liquor will be present as caustic soda and the remainder mainly assodium thiosulfate, or

as sodium sulfite and sodium thiosulfate.

- A cooking liquor may thus be used containing at least 40 gr. of sodiumper liter, pf which at least40% is present as sodium hydroxide and atleast 5% as sodium thiosulfate, or as sodium sulfite and sodium thiosulfate, with the articular amounts of caustic soda and so iumthiosulfate, or of sodium thiosulfate and sodium sulfite, varyingsomewhat above these percentages. The amount of cooking liquor ma beabout 700 to 1100 gallons or a cord 0 wood (measured before chipping),the liquor containing the higher percentages of caustic soda being usedin smaller amount, and those containing the smaller percentages ofcaustic soda being used in larger amount. By the use of such an alkalinecooking liquor containing thiosulfate, or thiosulfate and sulfite, it ispossible to produce satisfactory pulp or cellulose material from forestprod nets and other cellulose-bearing materials which, due to theirinherent composition and properties, have been unsuited to theproduction of high grade cellulose material by the processes heretoforecommonly practiced. Materials such as woods and other forest material ofinferior value (for treatment according to common methods) as well asmaterials such as bagasse, reeds, grasses, bamboo co'rnstalks, straw,etc., can advantageously be subjected to digestion with such a'lkalinethiosulfate, or sulfite and thiosulfate, cooking liquor and high gradepulp or cellulose material produced therefrom.

This method, therefore, increases the available supply of raw materialsfor the ductlon of high grade pulp or cellulose products.

In carrying outthe digestion with such an alkaline thiosulfate liquor,or with such an alkaline sulfite and thiosulfate liquor, the time oftreatment and the temperature, pressure, etc.', can be varied dependingupon the particular wood or other material un dergoing digestion; butthe process can becarried out under similar conditions of temperatureand pressure to those commonly used in the soda process, e. g., byheating the digester by direct steam at a pressure which may vary forabout 90 to 140 lbs, and with circulation of the liquor within thedigester by the steam duringthe digestion. The digestion will, however,be modified by the action of the composite cooking liquor so "that lessinjury to the cellulose material will take place and so that a superiorpulp or cellulose material will be produced.

According. to the present invention, accordingly, the alkaline cookingliquor may be composed of caustic soda and sodium thioslufate, or it maybe composed of three ingredients, namely, caustic -soda, sodium sulfiteand sodium thiosulfate. The liquor may also contain other compounds than4 prothose mentioned, such, for example, as sodium sulfate, sodiumcarbonate, or sodium sulfide.

Our investigations have shown that if some untreated black liquor ismixed with new cooking liquor containing caustic soda,

a portion of the caustic soda is used up in the formation of othersodium compounds by reaction either directly or indirectly between thecaustic soda. and soluble organic compounds, so that the total contentof caustic soda is not available for cooking the wood chips in the sameway that it would be if no such soluble organic constituents werepresent. Sodium sulfite and sodiumthiosulfate exert a retardinginfluence upon the reaction between the caustic soda and the solubleorganic compounds, and likewise upon the cellulose, so that the causticsoda can act more efiectively, and so that the destructive action forthe same total amount of caustic soda is minimized.

The present application is a division of our 'r1or application, SerialNo. 456187, filed arch 28, 1921.

We claim:

1. The improvement in the production of pulp, which comprises subjectingthe wood chips in the digester to the action of a cookliquor containingcaustic soda and,

m sodium thiosulfate, thecaustic soda being present in preponderatingamount.

2. In the preparation of chemical pulp, the use of a cooking li uorcomprising sodium hydroxide and so ium thiosulfate, the sodium hydroxidebeing used materially in excess of the amount, required to decomposesilicates and aluminates. in the material treated.

3. In the preparation of chemicaljpulp,

the use of a cooking liquor comprising a hydroxide and athiosulfate,-the hydroxide being used materially in excess of the amountrequired to decompose silicates and aluminates in the material treated.

4. In the preparation of chemical pulp,

the use of a cooking liquor comprising a 7. The improvement in theproduction of pulp, which comprises subjecting wood chips to digestionwith a-cooking liquor containing caustic soda and sodium thiosulfate,the cooking liquor containing at least 40 grams of sodium per liter, ofwhich at least 40 per cent is present as sodium hydroxide and at least 5per cent as sodium thiosulfate.

8.' The method of minimizing the destruc live action of caustic sodaupon the soluble organic compounds of wood in the cooking of wood chips,which comprises cooking the chips with a caustic soda cooking liquor containing sodium thiosulfate in amount less than that ofthe caustic soda.

In testimony whereof we hereunto afiix our signatures.

LINN BRADLEY. EDWARD P. MoKEEFE.

